By Tim Kelly and Phil Stewart
TOKYO/WASHINGTON (Reuters) - Two unarmed U.S. B-52 bombers flew over disputed islands on a training mission in the East China Sea without informing Beijing while Japan's main airlines ignored Chinese authorities when their planes passed through a new airspace defense zone on Wednesday.
The defiance from Japan and its ally the United States over China's new identification rules raises the stakes in a territorial standoff between Beijing and Tokyo over the islands and challenges China to make the next move.
China published coordinates for an East China Sea Air Defense Identification Zone over the weekend and warned it would take "defensive emergency measures" against aircraft that failed to identify themselves properly. The zone is about two thirds the size of Britain.
"If the United States conducts two or three more flights like this, China will be forced to respond. If China can only respond verbally it would be humiliating," said Sun Zhe, a professor at the Center for U.S.-China Relations at Tsinghua University in Beijing.
"The concept of the paper tiger is very important. All sides face it."
China's Defense Ministry said it had monitored the entire progress of the U.S. bombers through the zone on Tuesday Asian time. A Pentagon spokesman said the planes had neither been observed nor contacted by Chinese aircraft.
Chinese Foreign Ministry spokesman Qin Gang, when asked how China would respond to future infractions of the zone, said the country would "make an appropriate response" that depended on the "situation and degree of threat".
Qin added that China had informed "relevant countries" before setting up the zone. He would not elaborate.
Following a request from the Japanese government, Japan Airlines and ANA Holdings said they stopped giving flight plans and other information to Chinese authorities on Wednesday. Neither airline had experienced any problems when passing through the zone, they added.
Japan's aviation industry association said it had concluded there was no threat to passenger safety by ignoring the Chinese demands, JAL said. Both JAL and ANA posted notices on their websites informing its passengers of their decision.
The flight by the B-52 bombers was part of a long-planned exercise, a U.S. military official said.
Some experts have said the Chinese move was aimed at chipping away at Tokyo's claim to administrative control over the area, including the tiny uninhabited islands known as the Senkaku in Japan and the Diaoyu in China.
The action might have backfired, said Brad Glosserman, executive director of the Honolulu-based Pacific Forum CSIS.
"This is confirming the darker view of China in Asia," Glosserman said. "The Chinese once again are proving to be their own worst enemy ... driving the U.S. closer to Japan and (South) Korea closer to the position of Tokyo as well."
U.S. Ambassador to Japan Caroline Kennedy, in her first speech since assuming her post earlier this month, criticized China's "unilateral action" as undermining regional security.
Kennedy also said Japan had shown "great restraint this past year" and urged Tokyo to continue to do so. "We encourage Japan to increase communication with its neighbors and continue to respond to regional challenges in a measured way."
BIDEN VISITS REGION NEXT WEEK
The Chinese action was also likely to bolster support in Japan for hawkish Prime Minister Shinzo Abe's agenda to strengthen the military and loosen the limits of the post-war, pacifist constitution on its armed forces.
While Washington does not take a position on sovereignty over the islands, it recognizes that Tokyo has administrative control over them and it is therefore bound by treaty to defend Japan in the event of an armed conflict.
The B-52s, part of the Air Force fleet for more than half a century, are relatively slow compared with today's fighter jets and far easier to spot than stealth aircraft.
"We have conducted operations in the area of the Senkakus. We have continued to follow our normal procedures, which include not filing flight plans, not radioing ahead and not registering our frequencies," Pentagon spokesman Colonel Steve Warren said.
The dispute comes before a planned trip to the region by U.S. Vice-President Joe Biden, who is scheduled to travel to Japan next week and also has stops in China and South Korea.
Annual U.S.-Japan naval exercises are also taking place in waters off the Japanese islands of Okinawa and Kyushu, to the east of China's new zone. The drills, which involve the USS George Washington aircraft carrier, recently taking part in the Philippine typhoon relief effort, were planned before China's announcement of the zone.
CHINA DEMANDS FLIGHT PLANS
The new Chinese rules mean aircraft have to report flight plans to China, maintain radio contact and reply promptly to identification inquiries and bear clear markings of their nationality and registration.
On Monday, civil aviation officials from Hong Kong and Taiwan said their carriers entering the zone must file flight plans. A transport ministry official in Seoul said South Korean planes would do the same.
Qantas Airways Ltd said on Wednesday its pilots would keep China informed of their flights through the area.
The United States and Japan have sharply criticized China's airspace declaration, prompting Beijing to lodge counter protests and warn Washington to stay out of the dispute.
An outspoken retired Chinese military figure, former Major General Luo Yuan, wrote on Tuesday that China should use force in the zone if needed, adding the United States especially had to comply or face the consequences. Some experts, however, questioned whether China had the military assets to fully implement the new measures.
While the zone is outside China's territorial airspace, the Chinese Defense Ministry has said its establishment had a sound legal basis and accorded with common international practices.
Other countries including the United States, Japan and South Korea have similar zones but only require aircraft to file flight plans and identify themselves if those planes intend to pass through national airspace.
In addition, China sent its sole aircraft carrier on a training mission for the first time into the oil- and gas-rich South China Sea on Tuesday, upsetting the Philippines.
China claims almost the entire South China Sea, conflicting with claims from Taiwan, Malaysia, Brunei, the Philippines and Vietnam.
(Additional reporting by Jeff Mason in California, David Alexander, Matt Spetalnick and Lesley Wroughton in Washington, Kiyoshi Takenaka in Tokyo, Ben Blanchard and Michael Martina in Beijing and Lincoln Feast in Sydney. Editing by Dean Yates and Nick Macfie)